In radio communication systems having portable radio devices, such as paging systems, personal radiotelephone systems, and portable two way radio systems, energy conservation is among the most important product design concerns, for the purpose of prolonging the duty cycle of the energy storage devices, which are generally batteries. Known means of accomplishing such energy conservation in portable radio devices, which have been used successfully, are the use of electronic devices chosen for their low power requirements, such as liquid crystal displays, the use of logic and radio frequency devices that operate at low voltages, such as one volt, and the use of low power modes whenever possible, including the shut down of the radio receiver when the portable device can establish that no information intended for the portable is being transmitted, such as in a synchronous or partially synchronous systems, wherein predesignated time slots are assigned to individual portable devices for at least a portion of the time.
However, the use of very long messages, such as news and stock market information, containing information intended for all of, or a large group of, the portable devices in a communication system, is becoming more common. In this case, the portable device is in the normal power mode during the long message and therefore does not conserve power very well.
Thus, what is needed is a means to conserve power in a portable radio device when long messages are being transmitted to the radio device.